by Huy Duong and Van Pham | CSIS Blog – On November 30, 2012, two Chinese trawlers operating just outside the Gulf of Tonkin ran across the seismic cable being towed by a Vietnamese survey ship and severed it. Vietnam sent a diplomatic note to China’s embassy in Hanoi to protest. In response, China claimed that this concerns an area of overlapping claims and demanded that Vietnam stop unilateral oil and gas activities.

This incident took place at 17º26’N, 108º02’E—roughly 43 nautical miles from Vietnam’s Con Co Island, 54 nautical miles from Vietnam’s mainland coast, and 75 miles from China’s Hainan Island. It was 210 miles from the disputed Paracel Islands, and is therefore unrelated to the dispute over that archipelago.

Although China and Vietnam agreed to a boundary between their waters inside the Gulf of Tonkin in 2000, the two countries are still negotiating a boundary for the area outside its entrance.

If international law or international practice of maritime delimitation is applied, there is little doubt that the negotiated boundary will be at approximately equal distance from China’s Hainan Island and Vietnam’s mainland coast and coastal islands.

If the boundary were drawn in a way that is most favorable to Vietnam (i.e., halfway between Con Co Island and Hainan), then the location of this incident would be 13.5 nautical miles nearer to the Vietnamese mainland coast than this boundary.

Conversely, if the boundary were drawn in a way that is most favorable to China (i.e., halfway between Vietnam’s mainland coast and Hainan, disregarding Vietnam’s Con Co Island), then the location of this incident would still be 10.5 nautical miles nearer to the Vietnamese mainland coast than this boundary.

A reasonable compromise would be for the boundary to lie exactly between the two above-mentioned positions. The location of the cable-cutting incident is 12 nautical miles nearer to Vietnam than this compromise boundary.

In claiming that the cable-cutting incident had taken place in an area of overlapping claims, China is claiming at least 12 nautical miles past the compromise boundary above, and 10.5 nautical miles past even the boundary that is most favorable to itself.

Thus far, China has not indicated the basis for this claim, but it would be difficult to find a legal justification for why a maritime area 75 nautical miles from Hainan and 54 nautical miles from Vietnam’s mainland coast should belong to China. It is apparent that China is seeking to treat an area that it cannot reasonably dispute as a disputed area, and there are three possible explanations for this.

It might be China’s negotiating tactic to claim far beyond all possible equidistance lines, so that when a compromise is reached it will still end up with a part of the area beyond those lines.

The second hypothesis is that China does not accept the use of equidistance lines for drawing the boundary for this area. In pursuing its various claims around the “U-shaped line”, China has been referring to “historic waters” and “historic rights”. It is possible that China wishes to apply these arguments to the demarcation of this area.

The third hypothesis is that China does not want to demarcate this area at all, preferring instead to “set aside the dispute and pursue joint development” even in an area where it does not have a reasonable claim.

Due to the asymmetry of power between the two countries, a negotiated boundary based on the use of equidistance lines, as per legal and international norms for the demarcation of similar areas, will best protect Vietnam’s rights. Joint development might be a temporary solution or might operate in conjunction with this boundary, but cannot be a viable long term substitute for it. Unfortunately, this asymmetry also means that Vietnam’s options might be limited should China choose one or a combination of the three above-mentioned scenarios.

Mr. Huy Duong contributes articles on the South China Sea to several news outlets including the BBC and Vietnam’s online publication VietNamNet.Ms. Van Pham contributes articles on the South China Sea disputes to the BBC.